1. Field of the Invention
The subject invention generally pertains to commercial and industrial equipment for the Heating, Ventilation, and Air Conditioning (H.V.A.C.) industry. In particular, the invention relates to an H.V.A.C. housing (also called an H.V.A.C. cabinet or unit) which is insulated with foamed insulation and composed of materials intended to create a thermal barrier to isolate the insulation from the interior of the building, in conformance with the International Building Code (I.B.C.).
2. Description of Related Art
Heat exchangers, compressors, blowers, filters and other H.V.A.C. equipment are often housed within an air handling enclosure. The enclosure helps shelter the equipment, provides a sound barrier, and perhaps most importantly, the enclosure provides a conduit for directing the air through the equipment. Air handling enclosures usually comprise a number of sheet metal panels that are interconnected to create a box-like structure.
The most current state of the art for H.V.A.C. enclosure design is an inner and outer layer of sheet metal enclosing a foam insulation core. Therefore, the current H.V.A.C. panel design can be described as a three-layer sandwich assembly composed of an inner liner (usually sheet metal), insulation (usually foam insulation, but occasionally fiberglass insulation, creating the core of the panel), and an outer liner (usually sheet metal). Reference is made to U.S. Pat. No. 7,526,903 (2005) which provides a description and drawings of the state of the art, and which is incorporated herein by reference.
In most cases, the panels are insulated to minimize heat loss between the interior and exterior of the enclosure. The primary functions of the insulation are to provide a reduction in sound transmission from the enclosed machinery into the surrounding space and to improve operating efficiency by minimizing undesirable heat loss or gain into the surrounding space. Insulation is rated according to its thermal resistance, or R-value, with a higher value being more desirable. In the past, fiberglass batt insulation has been used, and currently many major manufacturers have converted from using fiberglass batt to using some type of expanded foam insulation. Fiberglass batt can have an R-value varying from approximately 3.0 to 4.0 per inch thickness, and expanded foam insulation can have an R-value of anywhere between 4.0 and 7.5 or above, per inch thickness.
FIG. 4 illustrates a current state of the art panel composed of a polyurethane foam core 42 with an interior metal liner 41 and an exterior metal liner 43. The major disadvantages of using this type of barrier with an expanded foam insulation are the flame, smoke and chemical by-products generated by the foam during a fire. In addition, there is a tendency for the polyurethane foam core 42 to delaminate from its metal liners 41, 43.
Due to the fire and smoke characteristics of foam insulation, the I.B.C. requires that any foam insulation used in a building be isolated from the interior of the building by an approved thermal barrier. Sheet metal is not approved as a thermal barrier, and consequently the need exists for a panel design that can provide this barrier.
It is also appreciated that H.V.A.C. air distribution equipment operates with a static pressure differential across the housing walls. This pressure differential causes a deflection in the panels resulting in a slight bowing of the panels. This bowing puts high stress on the bond between the foam insulation and the metal of the panel, often leading to delamination and structural weakness.
It is also an object of the present invention to provide an air handling enclosure with self-supporting, insulated thermal panels using a core of foam insulation, and satisfying the current I.B.C. (2012) requirements for thermal barriers over foam insulation. This invention uses an engineered barrier between the inner and/or outer liners and the insulation to create a thermal barrier assembly.
Another object of the invention is to use a foam insulation core with an engineered honeycomb structural layer located between the core and the inner and outer liners.
Another object of the invention is to provide a thermal barrier for any type of insulation core, whether it is foamed in place or made of pre-manufactured sheets, and whether it be polyurethane, polypropylene, polyvinyl chloride (P.V.C.) or any other type of insulation for which the I.B.C. requires a thermal barrier.
Another object of the invention is to use fiberglass reinforced plastic inner and/or outer liners. Fiberglass reinforced plastic has a higher thermal resistance than steel or aluminum and therefore contributes to the properties of a thermal barrier. The use of fiberglass reinforced plastic liners allows a slight reduction in the thickness of the engineered barrier.
Another object of the invention is to use a chemical bonding agent, such as a resin between the polyurethane insulation, the structural core, and the panel outer walls. This embodiment may include a fiberglass weave, cloth, mat, or other porous material to help absorb resin and bond the polyurethane to the structural core.